The present invention relates to a blind rivet element having a setting head and a shank. The shank has a female thread or a receptacle for a threaded bolt at its end distal to the setting head, and a deformation section between the female thread or the bolt receptacle and the setting head. The setting head has a larger outside diameter than the shank. After deformation of the shank and creation of the closing head, the deformation section has a bead that extends on the exterior circumference of the shank.
Blind rivet elements of the above-noted type are designed for example as blind rivet nuts or blind rivet threaded bolts. EP 1 918 596 describes a blind rivet element of the type cited in the foregoing.
Blind rivet elements have proven appropriate for fastening tasks in which a screw connection is required in the area of thin-walled materials, for example metal sheets, into which it is not normally possible to cut a loadable thread. Blind rivet elements form the mating retainer flange, or closing head, by forming a bead that is in the form of a material fold. The lower the material strength of a thin-walled article, especially metal sheet, with which the blind rivet element of defined dimensions is to be connected, the greater the outer diameter of the bead. However, the radial extension of the bead is always relatively small with respect to the outer diameter of the shank of the blind rivet element.
DE 198 08 685 A1 also describes a blind rivet element of the type described above. It is embodied as a blind rivet nut. In this blind rivet nut, the area in the deformation section, where the closing head begins to be formed, is not defined. Instead, it depends in particular on the mounting arrangement. When the blind rivet nut is being set, a circumferential bead forms in the area of the deformation section. This bead is thus closed in the circumferential direction of the shank, and consequently describes a complete circle. The thin-walled article, especially metal sheet, is fixed between this circumferential bead and the setting head.
In order to attain a defined design of the circumferential bead, EP 1 918 596 A1 provides that the shank has a weakening in a central circumferential area of the deformation section. This weakening is attained in particular by means of a plurality of holes in the shank. After the blind rivet element has deformed, a closing head in the shape of a circumferential bead forms in a defined manner due to the weakening of the shank wall.
U.S. Pat. No. 3,789,728 describes another type of blind rivet element. In this case, the blind rivet element is embodied as a blind rivet nut. Its shank is provided with a plurality of through-slits arranged parallel to the center longitudinal axis of the shank. Consequently, no bead-like closing head is created when the blind rivet element is being set. Instead, rosettes are bent out of the material. These rosettes have quite a large radial extension compared to a bead. A wedge-shaped intermediate space forms between adjacent rosettes. Because of the large radial extension of the deformed sections of the blind rivet nut, its outer radial position on the metal sheet is quite a distance from the center longitudinal axis of the shank.
The above-described blind rivet elements may be connected to thin-walled articles, especially metal sheet, only if there is sufficient room behind the thin-walled element for the blind rivet element to deform radially outwardly in the area of its deformation section when the blind rivet element is set. This is particularly true for those embodiments of the blind rivet element that forms rosettes when they are set.